Re: [PATCH v3] x86/vmlinux: Fix vmlinux.lds.S with pre-2.23 binutils

H. Peter Anvin
2020-01-14T01:57:56Z

On 2020-01-13 17:53, Kees Cook wrote:>>
>> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
>> index 3a1a819da137..bad4e22384dc 100644
>> --- a/arch/x86/kernel/vmlinux.lds.S
>> +++ b/arch/x86/kernel/vmlinux.lds.S
>> @@ -144,10 +144,12 @@ SECTIONS
>> *(.text.__x86.indirect_thunk)
>> __indirect_thunk_end = .;
>> #endif
>> +
>> + /* End of text section */
>> + _etext = .;
>> } :text =0xcccc
>>
>> - /* End of text section, which should occupy whole number of pages */
>> - _etext = .;
>> + /* .text should occupy whole number of pages */
>> . = ALIGN(PAGE_SIZE);
>
> NAK: linkers can add things at the end of .text that will go missing from
> the kernel if _etext isn't _outside_ the .text section, truly beyond the
> end of the .text section. This patch will break Control Flow Integrity
> checking since the jump tables are at the end of .text.
>
> Boris, we're always working around weird linker problems; I don't see a
> problem with the v2 patch to fix up old binutils...
>

Why not add the marker into a separate section instead of leaving it as an
absolute "floater"? Very old binutils would botch that case, but I think that
has been long since addressed well below our current minimum version.

-hpa